The wikipedia entry on the trolls of Terry Pratchett's Discworld series explains that yeti are actually snow trolls.
Long-time readers of this blog know that it is a pet theory of mine. Be advised, I may be subject to a loss of objectivity because of my "affection" towards my pet theory.
Here's the quote from wikipedia:
Discworld yeti are a kind of troll, dwelling in the high Ramtops. They are noted for having thick, white, insulating rock-based fur, and large feet, which are considered an aphrodisiac in the Agatean Empire. At least some tribes are unaware that attempting to eat humans is considered inappropriate these days. Yetis have a hunting technique of lying still in the snow until their prey was near them, then pouncing.
The most surprising thing about yeti is their ability to manipulate time. A Yeti can "save" its life up to a certain point and, at the point of death, can return to that point, with the knowledge of what was going to kill it (a clear reference to video games Terry Pratchett is known to be a gamer). According to the History Monks, the entire species has been rendered extinct three times.